Zinc dust canister



June 12, 1934. P. M. 'GINDER ET AL ZINC DUST CANISTER Filed Jan. 14, 1953 .2 Sheets-Sheet l ATTORNEYS June 12, 1934. P. M. GINDER ET AL ZINC DUST CANISTER 4 2 Sheets-Sh'eet 2 Filed Jan. 14, 1933 INVENTOR$ G LJL- ATTORNEYS Patented June 12, I934 T' OFFICE ZINC DUST oAmsTER Philip M. Ginder and George F. Hall-acre, Palmerton, Pa., assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application January 14, 1933, Serial No. 651,827

9 Claims.

This invention relates to the manufacture of zinc dust and has for its object the provision of certain improvements in the condensation of metallic zinc vapor to zinc dust and the provision of an improved apparatus'therefor. More particularly, the invention contemplates an improved continuous method of making zinc dust of fine and uniform particle size and with a low zinc oxide content, as well as an improved ap- 10 paratus for the practice of that method.

I Zinc dust is finely divided metallic zinc. The zinc dust products of commerce usually contain small percentages of zinc oxide. The value of the zinc dust is dependent, to some extent at least, upon its metallic zinc content and is, for certain purposes, materially lessened by the presence of zinc oxide. One of the characteristic features of the present invention is that it permits the production of a zinc dust product containing a very small and practically negligible percentage of zinc oxide.

Zinc dust has heretofore been incidentally and unavoidably made as a by-product in the production of zinc in ordinary smelter furnaces, being collected in prolongs attached to the customary zinc condensers. This by-pi'oduct zinc dust is usually known as blue powder and is of inferior quality.

Commercial zinc dust is ordinarily produced by volatilizing metallic zinc in a retort or graphite bottle and conducting the resulting zinc vapor into a condenser or canister, where it is rapidly cooled to a temperature below the freezing point of zinc so as to form solid zinc dustrather than molten zinc. This operation is ordinarily carried out as a batch process, that is to say, it is discontinuous. The retort is charged with metallic zinc, and after the charge has been substantially volatilized, the retort is opened, the residue scraped out and the zinc dust produced is removed from the canister. The retort is then recharged and the cycle of operations is repeated. This batch operation entails the following specific disadvantages:

1. Excessive breakage of the retorts by thermal shock incurred during their periodic heating and cooling.

2. Loss of zinc in theretort residues, which must be scraped out after each operation.

3. Excessive oxidation of the zinc dust, due to the following circumstances:

(a) The canister is periodically filled with atmospheric oxygen during the operation of emptyi it.

(b Atniisph'eric air tends to leak into the canister during the last stages of the distillation, when the supply of zinc vapor decreases as the charge of metallic zinc in the retort approaches exhaustion.

(c) The relatively small amounts of zinc removed from the canister while hot readily become oxidized during the handling. 4. The distillation of the zinc is inefficient since the bath of molten metal gradually decreases during the operation and only a small quantity of zinc is present in the retort during the last stages of distillation.

On account of these factors, theoperating cost of thebatch method of zinc dust production as heretofore ordinarily practiced is high. The present invention aims to overcome the aforementioned difiiculties, and contemplates a continuous method of making zinc dust of fine and uniform particle size and with a low zinc oxide content. The invention is characterized by condensation of metallic zinc vapor to zinc dust in a substantially gas-tight chamber and under a substantially uniform and constant gas pressure. In our present preferred form of the invention, the substantially gas-tight condensing chamber or canister communicates with a reservoir'containing a gas inert to zinc vapor, such as nitrogen, and the volume of the reservoir is varied automatically in response to any changes in gas conditions in the chamber tending to vary the gas pressure therein.

The novel features of the invention will be best understood from the following description taken in conjunction with the accompanying drawings in which Fig. 1 is a side elevation of an apparatus embodying the invention, and

Fig. 2 is a top plan of the apparatus.

Referring to the drawings, there is diagrammatically indicated a furnace 5 of conventional construction having one or more zinc distillation retorts 6. A charging well 7 communicates through a conduit 8 with the interior of the retort. The retort 6 is connected to the zinc dust condensing chamber or canister 9 by a conduit 10, preferably positioned so as to slope upwardly from the retort to the canister as indicated in Fig. 1.

The canister 9 is preferably constructed of sheet iron with welded joints, except as hereinafter explained, and is appropriately mounted on masonry supports or the like. The canister illustrated in the drawings is of rectangular section inall three dimensionalplanes but may be of any appropriate configuration. The top of the canister is provided with a removable cap 11 seated in a fine sand seal 12. This sealed cap provides a safety valve for any'explosion that may occur within the canister.

The end of the canister adjacent the conduit 10 communicates at its bottom with a scrap zinc collecting pit 13. The opening between the canister and the pit 13 may be closed by a tight slide door 14. Access to the pit 13 is provided through a door 15. The bottom of the canister, beyond the pit 13, is provided with a series of depending hoppers 16, closed at the bottom by tight slide valves 16.

A gas line 1'7, provided with clean-out plugs 18, connects the end of the canister, remote from the conduit 10, with a gas reservoir 19. The gas reservoir consists of a cylindrical lower casing 20 within which vertically slides a cylindrical bell or top casing 21; the annular space between the two casings 20 and 21 being provided with a water seal 22. The bell 21 is counter-poised by a counterweight 23. The counterweight is enclosed in a housing 24 and is connected to the bell by a rope 25 passing over sheaves 26.

The zinc vapor conduit 10 extends into the canister through a plate 27 removably mounted on the end of the canister. Plates having different openings are provided to accommodate difierent sizes of conduits, thereby permitting variation in the size of the orifice for introducing zinc vapor into the canister. An opening 28 is pro- -vided in one side of the canister approximate the exit end of the conduit 10 in order to provide access to the conduit for keeping it clean 'and open. During normal operations, the opening 28 is closed by luting or the like. In order to permit increase in the length of the canister, if desired, the end wall, remote from the conduit 10, is attached to the sides, top and bottom walls by flanged ends 29 bolted or otherwise appropriately secured together. The other sheet metal joints in the canister construction are welded so that the canister as a whole is substantially gas tight.

In practicing the invention in the apparatus illustrated in the drawings, an appropriate volume of molten zinc metal is constantly maintained in the retort 6 by periodically supplying molten metal to the retort through the charge well 7. The molten zinc metal is progressively evaporated by heat supplied fromthe furnace and the resulting zinc vapor passes through the'upwardly directed conduit 10 into the canister 9. Any relatively large particles or droplets of zinc that may be formed by condensation of vapor in the conduit 10 flow back through the conduit into the retort, in consequence'of the slope of the conduit. Relatively large droplets of molten zinc are thus prevented from entering the canister. Any coarse particles of zinc that form immediately after the zinc vaporenters the canister descend upon the slide door 14. From time to time the slide door 14 is manipulated to permit the coarse particles accumulating thereon-to drop into the scrap collecting pit 13, and this scrap zinc is removed from the pit through the door 15 as desired or necessary. The finer commercial zinc dust settles in the hoppers 16, the finer product being collected in the hoppers more remote from the zinc vapor conduit 10. The zinc dust product is periodically withdrawn from the hoppers by manipulation of the slide valves 16' which may, if desired, be constructed as double slide valves, one above the other. D 1 The canister 9 and gas reservoir 19 are prefer ably filled with an appropriate gas inert to zinc vapor before starting the operation of producing zinc dust. For example, the canister and reservoir may be filled with nitrogen. If desired, the operation may be commenced with the canister and reservoir filled with atmospheric air, in which case the air will soon be deprived of its oxygen content by oxidation of zinc vapor to zinc oxide.

The zinc oxide thusinitially produced is prefer-' 'or lower the operating gas pressure therein.

Thus, when the gas pressure within the canister decreases for any reason (such, for example, as a decrease in the rate of volatilization of zinc, due to the introduction into the retort of relatively cool zinc metal from the charging well 7), the gas and vapor within the canister tend to contract in volume on account of cooling. The reduced pressure resulting from such contraction in gas volume would tend to permit air to enter through any joint that might not be entirely gastight, if it were not for the supply of nitrogen, or

other appropriately inert gas, that is then supplied to the canister from the gas reservoir. When the canister again heats up, gas is forced back into the reservoir. The movable bell 21 of the gas reservoir automatically permits the volume of the reservoir to change in response to varying gas conditions within the canister, while at the same time maintaining a substantially constant gas pressure within the canister. This gas pressure within the canister is slightly in excess of the atmospheric pressure to minimize the possibility of air entering the canister through joints that may not be perfectly gas-tight.

The zinc dust product produced in accordance with the invention is fine in particle size and contains over 98% metallic zinc. The particle size of the zinc dust varies inversely with the volume of the canister, so that the particle size can becontrolled in practice by varying the volume of the canister. Thus. with a canister volume of 200 cubic feet in which 2000 pounds of zinc dust were condensed per day of twenty-four hours, there was produced, in the actual practice of the invention, a zinc dust product of which 99% passed through a 325 mesh standard screen. With a canister 90 cubic feet in volume operating under the same conditions, 92 to 93% of the zinc dust product passed through a 325 mesh screen. The zinc dust collected in the hoppers near the point of entrance of the zinc vapor is relatively coarser in particle size than the zinc dust collected in the hoppers more remote from the point of entrance of the zinc vapor, and consequently it is thus possible to produce zinc dust of graded particle sizes.

;We claim:

1. The improvement in the condensation of metallic zinc vapor to zinc dust, which comprises condensing the zinc vapor to zinc dust'in a substantially gas-tight chamber, and maintaining through the medium of a gas inert to zinc vapor a substantially constant gas presure within said chamber.

2. The improvement in the condensation of metallic zinc vapor to zinc dust, which comprises condensing the zinc vapor to zinc dust in a substantially gas-tight chambercommunicating with a reservoir containing a gas inert to zinc vapor, and maintaining the pressure of the gas in said reservoir substantially constant.

3. The improvement in the condensation of metallic zinc vapor to zinc dust, which comprises condensing the zinc vapor to zinc dust in a substantially gas-tight chambercommunicating with a reservoir containing a gas inert to zinc vapor, and maintaining in said reservoir a substantially constant gas pressure slightly in excess of the atmospheric pressure.

4. The improvement in the condensation of metallic zinc vapor to zinc dust, which comprises condensing the zinc vapor to zinc dust in a substantially gas-tight chamber communicating with a reservoir containing a gas inert to zinc vapor, and maintaining a substantially constant gas pressure within said chamber by automatically varying the volume of said reservoir in response to a change in gas conditions in the chamber tending to vary the gas pressure therein.

5. The improvement in the condensation of metallic zinc vapor to zinc dust, which comprises condensing the zinc vapor to zinc dust in a substantially gas-tight. chamber communicating with a reservoir containing a gas inert to zinc vapor, and maintaining in said chamber a substantially constant gas pressure slightly in excess of the atmospheric pressure by varying the volume of said reservoir in response to changes in gas conditions in the chamber tending to vary the gas.

pressure therein.

6. The combination with a substantially gastight canister for the condensation of metallic zinc vapor to zinc dust, of a gas reservoir coma municating with the canister and having means for maintaining a substantially constantgas pressure within the canister. j I

l. The combination with a substantially gastight canister for the condensation of metallic zinc vapor to zinc dust, of a gas reservoir commu-:

nicating with the canister, and means operatively 1 container having an inlet for zinc vapor at one' end thereof and 'zinc dust collecting means in the bottom thereof, the end of the container remote from said zinc vapor inlet being secured to the adj acent parts of the container by bolts while substantially all other joints of the container are welded.

PHILIP M. GINDER.

GEORGE F. HALFACRE. 

